Process of dewaxing oils



Nov 2, 1937. E. Ml D'oNs Er AL.

PROCESS OF DEWAXING OILS Filed May 5, 1934 2 Sheets-Sheet 1 Nov 2, 1937. E M DONS ET AL 2,097-,999

PROCESS OF DEWAXING OILS Filed May 5, 1934 l 2 Sheets-Sheet 2 Patented Nov. 2, 1937 UNITED STATES PATENT OFFICE PROCESS OF DEWAXING OILS Eddie M. Dons and Dwight B. Mapes, Tulsa, Okla.,

assignors to Mid-Continent Petroleum Corporation, Tulsa, Okla., a corporation of Dela- Waffe Application May 3, 1934, SerialNo. 723,662

4 Claims.

, suchas propane, is employed.

There are substantial variations in the nature of wax-containing oil stocks, and many valuable lubricating oil stocks cannot be economically dewaxed by the usual methods which comprise diluting the oil with naphtha, chilling the resultant solution, `and centrifuging, or slowly filtering,

the wax from the oil.

It has been proposed to employ propane as a chilling medium and a diluent during the dewaxing of oils. Propane is a naturally occurring hydrocarbon which is a gas at ordinary conditions of temperature and pressure, but can be converted into a liquid by subjecting the same to a relatively high pressure; Y

Substantially all lubricating oil stocks may be dewaxed with the proper use of propane, and such a process will more completely remove the waX than the old methods now in common use.

Lubricating oil stocks containing waX, when warm, can be readily dissolved in liquid propane, and a solution of undewaxed oil and propane can be chilled by evaporating some of the propane fromv the solution, the propane taking up heat from the solution as the propane passes into a vapor state. As the solution is chilled, wax crystals form which can be completely removed from the solution by filtering if the proper conditions of chilling have been maintained.

The method of chilling the solution of oil and propane is Very critical, and if the solution has not been properly chilled the wax cannot be successfully filtered from the solution.

Due to the critical condition of chilling, it has been thought that the batch operation of chilling Awas the only manner in which the proper chilling couldv be obtained. A batch operation provides satisfactorly conditions for chilling the solution of oil and propane, as the propane may be released from a large volume of the solution at the desired rate to precipitate the wax in the best form for filtering.

However, in a large commercial dewaxing plant, such batch operations have serious disadvantages. Large vessels of alloyv steel subjected to a high pressure must be repeatedly warmed and then chilled to about 40 F., which is an uneconomical and ineiicient procedure. Moreover, the hazards involved in such rapid temperature changes in high pressure vessels, necessitates Va very expensive construction.

vIn addition to the foregoing disadvantagesV the llutiorn passes through the passageway, propaneV (Cl. ISG-18) volume of propane required is large and the production slow.

An object of our invention, therefore, is to provide a continuous process for dewaxing an oil with propane wherein a constantly owing stream of the solution of oil and propane is continuously chilled at the desired rate and under conditions that result in a chilled solution fromwhich the waxv can readily be removed by filtration.

Another object of this invention is to provide a process wherein the temperature at any point in the system will be practically constant so as to avoid the strain of frequent and rapid temperature changes.

A further object is to provide a simple and relatively inexpensive process for dewaxing an oil with propane whileY obtaining a large production of dewaxed oil with a relatively small quantity of propane in the system.

'With the foregoing and other objects in View, the invention comprises the novel method hereinafter more specically described and shown in the accompanying drawings, which illustrate one form of the invention. However, it is to be understoodthat the invention comprehends changes, variations and modifications which come within the scopeV of the claims hereunto appended.

In the art of dewaxing oils with propane, it is well known that sudden or shock chilling by flash expansion of the solution of oil and propane results in precipitation of wax in a form that will not lilterffreely. The development of a continuous process must, therefore, provide for the desired chilling of the oil without sudden eX- pansion or evaporation of propane from the solution.

We have-found that the required gradual reduction in temperature and pressure can be obtained by passing the solution through an elongated passageway, preferably a coil of pipe, of 40 such length and diameter that the pressure necessary to maintain relatively Warm propane in a liquid state is very gradually reduced to atmospheric or nearly atmospheric pressure. The chilling passageway may be of uniform diameter throughout its length, but a more uniform pressure drop and more uniform rate of chilling is obtained by gradually increasing the diameter of the passageway toward the low` pressure end. As the solutionflows through the elongated chilling 50 passageway, a gradual loss of pressure occurs due to resistancerto flow in the passageway. Since the pressure is very gradually reduced as the sowill continually be passing from the liquid to the 5 vapor state, thus taking up heat from the solution. This propane vapor flows through the passageway with the solution, probably more or less in the form of foam, and as the volume increases due to increased vapor phase, the diameter of the pipe is preferably increased.

Advantages are gained by discharging regulated quantities of propane gas at various` intervals along the length ofthe chilling passageway, to effectively control the gradual reduction in pressure, this being especially true if the passage- Way is uniform in diameter throughoutv its length.

However, the preferred form of the inventionV is to use a coil of gradually increasing diameter, and when a very accurate control is desired, por- `tions of the vapor may be discharged at various points in the coil.

Fig. 1 is a diagrammatical View of a system embodying the features of this invention.

Fig. 2 is a detail view of a chilling coil adaptedfor use in the system. Y

As an illustration of one form of the invention, we have shown a system wherein undewaxed oil is continuously withdrawn Yfrom aast'orage tank l by pump 2 and passed` through'heater 3, and conductors and E into a mixing nozzle 6. 'Ihe oil is preferably warmed in the. heater@ to a temperature at which it is freely soluble with liquid propane, suchY as 175 F.

Liquid propane is continuously withdrawn from storage tank 'l bypump 8` and forced under a pressure suflicient to maintain the propane in a liquid condition through, conductors'S, I0 and 5 to the mixing nozzle@ where it is intimately mixed with the warm oil from storage tank I. The warm solution, which may be about one part oil to three parts' propane,v may be transmitted to a mixing nozzle EI where it is thoroughly mixed with a cold stream'of filter wash containing about two parts propane and a very small quantity of oil obtained from a source to be hereafter described. The resultantsolution is. trans- Initted through the conductor 5, which is Yprovided with a pressure'reducing valve 5 .to a solution reservoir i2. As a result of the addition of the relatively cold lter wash the solution upon entering the reservoir I2 will be ata. temperature of about 60 F. and contains approximately one part oil to ve parts propane.

From the reservoir i24 a stream of the's'olution may be continually forcedVV to one or;l more of the chilling coils ifi. IEach of the chilling coils has a suiicient lengthk and diameter to provide a gradual decrease in pressureV onk the solution whereby a portion of the 'propane is evaporated to effect a gradual reduction in the temperature as the stream passes through the v,pipe or passageway i 13;. v

As a specic illustration of one form of a chiller, we have shownin Fig. 2 a series of connected pipes having different diameters to provide an elongated passageway having a gradual increase in diameter. Starting at the high pressure end I3 of the chiller i4, the" connected pipes may have the following dimensions, 25feet of 1A; inch pipe as shown at A', 100 feet of inch pipeshown at B, feet of 1A; inch pipe-'shown at C, 100 feet of T5@ inch pipe shown at, D, 80 feet 'of LA; inch pipe shown at E, 40, feet of 1/2' inch pipe shown at F, and 40 feet of 5/8 inch pipe shown at G.

To Vprovide foravery accurate control of the gradual reduction in pressure on the stream. passing through the coil, or elongated passage-'f Way, Iii, we have shown vapor chambers I6 interposed at intervals along ,the coil. Each of these chambers i6 is provided with a discharge pipe II from which propane vapor may be transmitted through conductors I8, I 9 and 20 (Fig. l) to a compressor 2l, which forces the propane through condenser 22 and thence through pipes 23 and 24 to the propane storage tank 1. Each of the discharge pipes on the respective vapor chambers It (Fig. 2) may be provided with a valve 25 so that the operator may regulate the discharge of the propane vapor to maintain the desired gradual reduction in pressure on the s0- lution.v The pressures at dierent points in the chiller are indicated by gauges 26 (Fig. 2).

The continuous stream of solution entering the coils I4 from the reservoir I2 may be under a pressure of about 81 pounds per square inch and is gradually reduced so that the solution leaves the, coils at about atmospheric pressure.

The reservoir i2 may be provided with a propane vapor outlet ipe 59 leading to the conductor I9 froniwhich the vapor is returned through conductors 2li, 23 and 24, and compressor 2l, to the storage tank 1. The outlet pipe 5S on reservoir I2 is provided with a valve 59 which may be regulated to maintain the desired pressure on the solution in the reservoir i2, and also the pressure on the solution at the inlet pipes E3 of the chilling coils.

To provide for variations in the capacityA of the system, any one of the coils Iii` may be dispensed with by closing valves I5 and I5' associated therewith.

The solution leaving the chilling coils I may have been gradually reduced by the evaporation of propane to a temperature from 40 to 44 F., and is transmitted through conductors 2 and 2E to a receiver 29. The vaporized propane is separated from the solution4 in the receiver 29 and is removed through conductors 38 and 2i) leadingv tothefcompressor 2|, and returned to the propane storage tank through conductors 23 and` 24.

The'cold solution of propane and oil in the receiver 2S is forced throughI conductor 3l, and one of the branch conductors 32 by the pump 33 to one of the filters Sli. The branch conductors 32 are provided with valves 3,5 so that the solution may be diverted from one lter to the other when the lter in service becomes clogged with wax.

The coldA wax free solution flows. from filters 34 through a conductor Si?. to a receiver3,1 from which it is pumped through conductor 38 to a solvent recovery station, 3 9. At the. solvent recovery station 3S the propane may be recovered by any suitable method, such as byV heating the solution, reducing the pressure on the heated solution, and stripping with live steam. The recovered propane is withdrawn through a conductor fis, leading to the conductor ZEiand, after being condensed, is returned to the propane storage tank The dewaxed oil passes. from the solvent recovery station through a pipe 42, to a storage tank 43.

As previously stated, the cold solution of propane and oil in receiver Z may be transmitted to either of the lters soV that when the lter in service becomes cloggedwithwax the other filter is lavailable to prevent an interruption of the continuous sequence of the system,

When one'of the lters` becomes clogged, the Wax therein lis preferably treated with propane to wash the oil from-the wax. cakey in the filter.

To provide for the removal ofthe oil from the wax in the filter out of service, propane from storage tank may be passedthrough conduc-1 tors 9 and 45 to propane chilling coils 44. The

liquid propane leaving storage tanky l' may be at 100 F. It is, therefore, preferably cooled to about 0 F. at a heat exchanger 46, While flowing through the conductor 45. The chilled oil passing from the receiver 3l' to the propane recovery station may be advantageously used as the chilling medium in the heat exchanger 46. By closing a valve 4'! in the conductor 3E and opening valves 48 in a conductor 49 passing through the heat exchanger 46,;the cold solution will be diverted through said heat exchanger.

The propane, upon leaving the chilling coils 44, may be at a temperature oi' 40 to 44 F., and is transmitted to a reservoir 55. The gaseous propane in said reservoir 50 may be compressed and returned to the storage tank 1 through return conductors 5I, 2U, 23 and 24. The cold liquid propane may be pumped from the reservoir 55 through pipe 52, and by regulating the valves 53 and 35 in the respective branch conductors 32, the propane may be passed into the iilter out of service to wash the oil from the Wax cake.

The cold filter wash passes from either of the lters 34, through a pipe 54, and a pipe 55 to a reservoir 55 from which the cold iilter wash containing about two parts propane and a Very small quantity of oil is pumped through a conductor 51 to the fresh stream of solution flowing through conductor 5 so as to cool the fresh through a conductor 65 to a storage reservoir 64.l

If it is found desirable to add cold liquid propane to the chilled oil solution in the receiver 29, propane from reservoir 50 may be added in the desired quantity, through pipes 56 and 28 by a regulation of a valve El in the pipe B6.

As an example of the results obtained by a process and apparatus conforming to this invention, we treated a wax-containing heavy lubricating oil distillate with the following specication.

Gravity 24.0 Flash 495 Fire 560 Viscosity at 210 F 68.5 Cold test 92 This stock Was dissolved in propane in the ratio of one part stock to 'live parts of propane by volume and allowed to expand through the chilling coil, entering at 81 pounds pressure and expanding to atmospheric pressure at the outlet. The expanded solution was then filtered through No. 8 canvas, and the propane evaporated from the stock.

The dewaxed stock showed the following tests:

Gravity 23.5 Flash 490 Fire 560 Viscosity at 210 F 75 Cold test -18 ,A lter rate of approximately two gallons of stock per square foot per hour was obtainable at ten pounds lter pressure.

, While we have given a specific illustration of one process and apparatus, it is understood that numerous. changes and modifications may be madev without departing from the spirit of this invention, as set forth by the claims.

It is also understood that the term propane, does not necessarily imply a. pure propane, as propane is employed to cover a mixture of propane and, other hydrocarbons. For example,v a mix-'- ture comprising about per cent propane and about 20 per cent of ethane and butanes is quite satisfactory for carrying out this invention.

As previously stated, propane is a normally gaseous hydrocarbon, and in the preferred form of this invention we prefer touse propane as the normally gaseous hydrocarbon for treating the oil. However, other normally gaseous hydrocarbons include ethane, propylene, and isobutane.

This invention provides a very elective and efficient process for the continuous dewaxing of an oil with a normally gaseous hydrocarbon. The hazard of high pressure vessels, except for storage purposes, is eliminated. The equipment employed to carry out this process is not subjected to the strain of frequent temperature changes, as the temperature at any given point in the system is practically constant after the system is in operation.

The total volume of propane in the system is relatively small and the production of dewaxed oil relatively large. Moreover, the cost of the plant is relatively inexpensive and the dangers of the usual batch propane dewaxing plants are materially reduced.

We claimt- 1. The process of dewaxing oils which comprises dissolving a wax-containing oil in propane while subjecting the solution to a pressure sulcient to maintain Vthe propane in a substantially liquid condition, forcing a continuous stream of the resultant solution through an elongated passageway to gradually evaporate propane from the solution, thus providing a gradual decrease in the temperature of the solution as it progresses along said passageway, filtering the congealed wax from the oil, Washing the congealed wax with cold liquid propane to remove oil therefrom, and transmitting the resultant cold liquid propane into said continuous stream at a point in advance of said elongated passageway so as to suddenly cool said continuous stream before it reaches said passage- Way.

2. The process of dewaxing oils which comprises dissolving a wax-containing oil in a liqueiied normally gaseous hydrocarbon, suddenly cooling the resultant solution by introducing a i stream of chilled normally gaseous hydrocarbon liquid into a stream of said solution, thereafter precipitating wax from the cooled oil while forcing a stream of the resultant material through an elongated passageway to provide a gradual decrease in pressure on the owing stream and a gradual evaporation of a portion of the normally gaseous hydrocarbon, and separating the precipitated wax from the oil.

3. The process of dewaxing oils which comprises dissolving a wax-containing oil in propane while subjecting the solution to a pressure suicient to maintain the propane in. a substantially liquid condition, suddenly cooling the resultant solution by introducing a stream of chilled propane into a stream of said solution, thereafter precipitating Wax from the cooled oil While forcing a stream of the resultant material through an elo-ngated passageway to provide a gradual decrease in pressure on the flowing stream` and a gradual evaporation of a portion of the propane, and separating the precipitated Wax from the oil.

4. The process of dewaxing oils which comprises dissolving a Wax-containing oil in propane While subjecting the solution to a pressure sumcient to maintain thev propane in a substantially liquid condition, suddenly cooling the resultant solution by introducing a stream of chilled normally gaseous hydrocarbon liquid into a stream of said solution, thereafter precipitating Wax from the cooled oil while forcing a stream of the resultant material through an elongated passage- Way having a gradual increase in diameter to provide a gradual decrease in pressure on the owing stream and a gradual evaporation of a portion of the propane, and separating the precipitated Wax from the oil.

EDDIE M. DONS. DWIGHT B. MAPES. 

